The most efficient and economical way to debark logs is with the horizontal drum debarker. The drum debarker has a continuously rotating drum which rotates groups of logs so they rub against each other to remove the bark from the logs without any appreciable wear to the drum. To obtain good debarking efficiency, at least several logs must be in the same axial region of the drum, so they can rub against each other to remove the bark. The logs are usually fed into the drum in a continuous stream of groups of logs from an elevated curved hopper at one end of the drum and slide by gravity into the drum.
A hopper dimensioned to feed groups of relatively short logs of up to perhaps fifteen feet in length into the drum, does not work well with longer logs. Very long logs such as tree length logs, tend to jam and are bent by the hopper and drum when their lower ends enter the drum and the logs begin to rotate while their upper ends are still above the hopper inlet. Long logs in this position are rotated by the drum and are often damaged by rubbing against the hopper inlet, and the resultant reverse bending sometimes causes such long logs to break.
While it may be possible to efficiently debark tree length logs by using a much larger hopper, such a hopper would be very high and difficult to feed logs into, the hopper would be quite expensive, and shorter logs would not feed efficiently through such a larger hopper.
Thus, it has been necessary in the past to cut or slash tree length logs to shorter debarking length, before feeding the logs into the hopper. However, the saw used for cutting or slashing logs is costly to install and maintain, and there is some kerf i.e., blade width loss when logs are cut with a saw.
Other disadvantages of shorter logs is that there are more ends, which are subject to brooming, shorter logs often tumble in the debarking drum which causes more end damage, and shorter logs are less efficiently chipped, and yield less usable lumber.
On the other hand, debarked tree length logs provide a higher yield of usable lumber, and a higher yield of high quality uniform size chips for pulp can also be obtained from debarked tree length logs.
The problem has been that there was previously no efficient reliable way to debark tree length logs with a drum debarker.
In addition to directing relatively short logs into the drum, the hopper for such logs performs a containment function on the logs entering the drum. As the leading ends of the logs enter the continuously rotating drum and engage the inside of the drum, the logs begin to rotate while they are partly in the hopper. Such rotation sometimes causes additional rotation of upstream logs in the hopper by friction, and often causes a somewhat violent whipping motion of the logs entering the drum, which is resisted and contained by the upstream logs in the hopper and the thick walls of the hopper.
It has been proposed to feed tree length logs into a debarking drum with a nearly horizontal conveyor. To obtain efficient debarking, the tree length logs must be fed in groups of stacked or side by side logs. The problem with this technique is that the very long logs, perhaps sixty feet in length, begin to rotate and tumble soon after their leading ends enter the drum, while substantial lengths of the logs are still on the conveyor. The rotating and flailing motion of the logs can cause severe damage to the conveyor chain, and the trailing ends of logs leaving the conveyor can catch on and can be grabbed by the downwardly and rearwardly moving return portion of the conveyor. This can cause the trailing end of a log to be pushed down and pulled rearwardly so that the log jams in the chain while its leading end is whipped around by the drum. While the conveyor chain is quite strong and can support and move groups of heavy logs, localized stress in individual links caused by impact, or by grabbing a log at the nose end of the conveyor can damage the chain.
A further problem is that logs partly in the drum which are rotating tend to rotate trailing logs on the conveyor by friction.
There is therefor, a need for an efficient and reliable technique and apparatus for debarking logs of virtually any length, including tree length logs, in a rotating drum debarker.